Light-emitting device, electronic appliance, and lighting device comprising a light-emitting element having optimized optical path length

ABSTRACT

A light-emitting device and a lighting device each of which includes a plurality of light-emitting elements exhibiting light with different wavelengths are provided. The light-emitting device and the lighting device each have an element structure in which each of the light-emitting elements emits only light with a desired wavelength, and thus the light-emitting elements have favorable color purity. In the light-emitting element emitting light (λ R ) with the longest wavelength of the light with different wavelengths, the optical path length from a reflective electrode to a light-emitting layer (a light-emitting region) included in an EL layer is set to λ R /4 and the optical path length from the reflective electrode to a semi-transmissive and semi-reflective electrode is set to λ R /2.

This application is a divisional of copending U.S. application Ser. No.13/439,329, filed on Apr. 4, 2012 which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting device and a lightingdevice which utilize electroluminescence.

2. Description of the Related Art

In recent years, research and development have been extensivelyconducted on light-emitting elements utilizing electroluminescence (EL).In a basic structure of such a light-emitting element, a layercontaining a light-emitting substance (an EL layer) is interposedbetween a pair of electrodes. By voltage application to this element,light emission can be obtained from the light-emitting substance.

Since such a light-emitting element is of self-light-emitting type, itis considered that the light-emitting element has advantages over aliquid crystal display, such as high pixel visibility and the eliminatedneed for a backlight. Accordingly, such a light-emitting element isthought to be suitable as a flat panel display element. Such alight-emitting element is also highly advantageous in that it can bethin and lightweight. Further, very high speed response is also one ofthe features of such an element.

Furthermore, since such a light-emitting element can be formed into afilm form, planar light emission can be easily obtained. Therefore, alarge-area element using planar light emission can be formed. This is afeature which is difficult to obtain with point light sources typifiedby incandescent lamps and LEDs or linear light sources typified byfluorescent lamps. Thus, the light-emitting element also has greatpotential as a planar light source applicable to a lighting device orthe like.

In order to apply such a light-emitting element to a light-emittingdevice, the light-extraction efficiency of the light-emitting elementneeds to be improved. As a method of improving the light-extractionefficiency of a light-emitting element, a structure in which a microoptical resonator (a microcavity) utilizing a resonant effect of lightbetween a pair of electrodes is used and regions having different cavitylengths are provided to improve the viewing angle dependence of alight-emitting element (e.g., see Patent Document 1), and the like havebeen proposed.

REFERENCE Patent Document

-   [Patent Document 1] Japanese Published Patent Application No.    2006-032327

SUMMARY OF THE INVENTION

Light-emitting elements utilizing a microcavity system are advantageousfor full color display. For example, unlike light-emitting elementswhich are separately formed depending on the colors R, G, and B, thelight-emitting elements utilizing a microcavity system do not need to beseparately formed depending on the colors R, G, and B; thus, higherdefinition can be easily achieved. As compared with a light-emittingelement using a color filter (CF) system, the light-emitting elementsutilizing a microcavity system can have low power consumption.

In the case where full color display is performed with thelight-emitting elements utilizing a microcavity system, it is necessaryto adjust the distance between a pair of electrodes in pixels for eachemission color. However, there is a problem in that color purity isdecreased in some pixels in which a plurality of wavelengths coexists.There is also a problem of an increase in the number of masks and stepsneeded for the adjustment of the distance between the pair ofelectrodes.

Thus, according to one embodiment of the present invention, alight-emitting device and a lighting device each of which includes aplurality of light-emitting elements exhibiting light with differentwavelengths and utilizes a microcavity system are provided. Thelight-emitting device and the lighting device each have an elementstructure in which only light with a desired wavelength is emitted fromeach of the light-emitting elements, and thus the light-emittingelements have favorable color purity and high light-extractionefficiency. Moreover, the number of steps and the cost are reduced.

According to one embodiment of the present invention, a light-emittingdevice and a lighting device each of which includes a plurality oflight-emitting elements exhibiting light with different wavelengths areprovided. The light-emitting device and the lighting device each have anelement structure in which only light with a desired wavelength isemitted from each of the light-emitting elements, and thus thelight-emitting elements have favorable color purity. In other words, inthe light-emitting element emitting light (λ_(R)) with the longestwavelength of the light with different wavelengths, the optical pathlength from a reflective electrode to a light-emitting layer (alight-emitting region) included in an EL layer is set to λ_(R)/4 and theoptical path length from the reflective electrode to a semi-transmissiveand semi-reflective electrode is set to λ_(R)/2.

As for a light-emitting device including three kinds of light-emittingelements emitting light (λ_(R), λ_(G), and λ_(B)) where the wavelengthrelation of λ_(R)>λ_(G)>λ_(B) is satisfied, a case where a firstlight-emitting layer emitting the light with the wavelength λ_(R), asecond light-emitting layer emitting the light with the wavelengthλ_(G), and a third light-emitting layer emitting the light with thewavelength λ_(B) are formed is described. In a first light-emittingelement emitting the light (λ_(G)), the optical path length from areflective electrode to the second light-emitting layer (G) (alight-emitting region) included in an EL layer is set to 3λ_(G)/4 andthe optical path length from the reflective electrode to asemi-transmissive and semi-reflective electrode is set to λ_(G). In asecond light-emitting element emitting the light (λ_(B)), the opticalpath length from the reflective electrode to the third light-emittinglayer (B) (a light-emitting region) included in the EL layer is set to3λ_(R)/4 and the optical path length from the reflective electrode tothe semi-transmissive and semi-reflective electrode is set to λ_(B). Ina third light-emitting element emitting the light (λ_(R)), the opticalpath length from the reflective electrode to the first light-emittinglayer (R) (a light-emitting region) included in the EL layer is set toλ_(R)/4 and the optical path length from the reflective electrode to thesemi-transmissive and semi-reflective electrode is set to λ_(R)/2. Inthis case, for adjustment of the optical path lengths, a firsttransparent conductive layer is provided between the reflectiveelectrode and the EL layer in the first light-emitting element, and asecond transparent conductive layer is provided between the reflectiveelectrode and the EL layer in the second light-emitting element. Notethat the first transparent conductive layer needs to be thicker than thesecond transparent conductive layer.

One embodiment of the present invention is a light-emitting deviceincluding a first light-emitting element including a first reflectiveelectrode, a first transparent conductive layer in contact with thefirst reflective electrode, an EL layer formed in contact with the firsttransparent conductive layer, and a semi-transmissive andsemi-reflective electrode formed in contact with the EL layer; a secondlight-emitting element including a second reflective electrode, a secondtransparent conductive layer in contact with the second reflectiveelectrode, the EL layer formed in contact with the second transparentconductive layer, and the semi-transmissive and semi-reflectiveelectrode formed in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer formed in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode formed in contact withthe EL layer. Light emitted from the third light-emitting element has alonger wavelength than light emitted from the first light-emittingelement and light emitted from the second light-emitting element.

One embodiment of the present invention is a light-emitting deviceincluding a first light-emitting element including a first reflectiveelectrode, a first transparent conductive layer in contact with thefirst reflective electrode, an EL layer formed in contact with the firsttransparent conductive layer, and a semi-transmissive andsemi-reflective electrode formed in contact with the EL layer; a secondlight-emitting element including a second reflective electrode, a secondtransparent conductive layer in contact with the second reflectiveelectrode, the EL layer formed in contact with the second transparentconductive layer, and the semi-transmissive and semi-reflectiveelectrode formed in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer formed in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode formed in contact withthe EL layer. The EL layer includes a first light-emitting layeremitting light with a wavelength λ_(R). The light with the wavelengthλ_(R) is emitted from the third light-emitting element. In the thirdlight-emitting element, the optical path length from the thirdreflective electrode to the first light-emitting layer is λ_(R)/4 andthe optical path length from the third reflective electrode to thesemi-transmissive and semi-reflective electrode is λ_(R)/2.

One embodiment of the present invention is a light-emitting deviceincluding a first light-emitting element including a first reflectiveelectrode, a first transparent conductive layer in contact with thefirst reflective electrode, an EL layer formed in contact with the firsttransparent conductive layer, and a semi-transmissive andsemi-reflective electrode formed in contact with the EL layer; a secondlight-emitting element including a second reflective electrode, a secondtransparent conductive layer in contact with the second reflectiveelectrode, the EL layer formed in contact with the second transparentconductive layer, and the semi-transmissive and semi-reflectiveelectrode formed in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer formed in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode formed in contact withthe EL layer. The EL layer includes a first light-emitting layeremitting light with a wavelength λ_(R), a second light-emitting layeremitting light with a wavelength λ_(G), and a third light-emitting layeremitting light with a wavelength λ_(B), where the wavelength relation ofλ_(R)>λ_(G)>λ_(B) is satisfied. The light with the wavelength λ_(G) isemitted from the first light-emitting element. In the firstlight-emitting element, the optical path length from the firstreflective electrode to the second light-emitting layer is 3λ_(G)/4 andthe optical path length from the first reflective electrode to thesemi-transmissive and semi-reflective electrode is λ_(G). The light withthe wavelength λ_(B) is emitted from the second light-emitting element.In the second light-emitting element, the optical path length from thesecond reflective electrode to the third light-emitting layer is3λ_(B)/4 and the optical path length from the second reflectiveelectrode to the semi-transmissive and semi-reflective electrode isλ_(B). The light with the wavelength λ_(R) is emitted from the thirdlight-emitting element. In the third light-emitting element, the opticalpath length from the third reflective electrode to the firstlight-emitting layer is λ_(R)/4 and the optical path length from thethird reflective electrode to the semi-transmissive and semi-reflectiveelectrode is λ_(R)/2.

Further, as for a light-emitting device including three kinds oflight-emitting elements emitting light (λ_(R), λ_(G), and λ_(B)) wherethe wavelength relation of λ_(R)>λ_(G)>λ_(B) is satisfied, a case wherea first light-emitting layer emitting light with a wavelength λ_(Y) anda second light-emitting layer emitting the light with the wavelengthλ_(B) are formed is described. In a first light-emitting elementemitting the light (λ_(G)), the optical path length from a reflectiveelectrode to the first light-emitting layer (Y) (a light-emittingregion) included in an EL layer is set to 3λ_(G)/4 and the optical pathlength from the reflective electrode to a semi-transmissive andsemi-reflective electrode is set to λ_(G). In a second light-emittingelement emitting the light (λ_(B)), the optical path length from thereflective electrode to the second light-emitting layer (B) (alight-emitting region) included in the EL layer is set to 3λ_(B)/4 andthe optical path length from the reflective electrode to thesemi-transmissive and semi-reflective electrode is set to λ_(B). In athird light-emitting element emitting the light (λ_(R)), the opticalpath length from the reflective electrode to the first light-emittinglayer (Y) (a light-emitting region) included in the EL layer is set toλ_(R)/4 and the optical path length from the reflective electrode to thesemi-transmissive and semi-reflective electrode is set to λ_(R)/2. Alsoin this case, for adjustment of the optical path lengths, a firsttransparent conductive layer is provided between the reflectiveelectrode and the EL layer in the first light-emitting element, and asecond transparent conductive layer is provided between the reflectiveelectrode and the EL layer in the second light-emitting element. Notethat the first transparent conductive layer needs to be thicker than thesecond transparent conductive layer.

One embodiment of the present invention is a light-emitting deviceincluding a first light-emitting element including a first reflectiveelectrode, a first transparent conductive layer in contact with thefirst reflective electrode, an EL layer formed in contact with the firsttransparent conductive layer, and a semi-transmissive andsemi-reflective electrode formed in contact with the EL layer; a secondlight-emitting element including a second reflective electrode, a secondtransparent conductive layer in contact with the second reflectiveelectrode, the EL layer formed in contact with the second transparentconductive layer, and the semi-transmissive and semi-reflectiveelectrode formed in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer formed in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode formed in contact withthe EL layer. The EL layer includes a first light-emitting layeremitting light with a wavelength λ_(Y). Light with a wavelength λ_(R) isemitted from the third light-emitting element. In the thirdlight-emitting element, the optical path length from the thirdreflective electrode to the first light-emitting layer is λ_(R)/4 andthe optical path length from the third reflective electrode to thesemi-transmissive and semi-reflective electrode is λ_(R)/2.

One embodiment of the present invention is a light-emitting deviceincluding a first light-emitting element including a first reflectiveelectrode, a first transparent conductive layer in contact with thefirst reflective electrode, an EL layer formed in contact with the firsttransparent conductive layer, and a semi-transmissive andsemi-reflective electrode formed in contact with the EL layer; a secondlight-emitting element including a second reflective electrode, a secondtransparent conductive layer in contact with the second reflectiveelectrode, the EL layer formed in contact with the second transparentconductive layer, and the semi-transmissive and semi-reflectiveelectrode formed in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer formed in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode formed in contact withthe EL layer. The EL layer includes a first light-emitting layeremitting light with a wavelength λ_(Y) and a second light-emitting layeremitting light with a wavelength 4, where the wavelength relation ofλ_(R)>λ_(Y)>λ_(G)>λ_(B) is satisfied. Light with the wavelength λ_(G) isemitted from the first light-emitting element. In the firstlight-emitting element, the optical path length from the firstreflective electrode to the first light-emitting layer is 3λ_(G)/4 andthe optical path length from the first reflective electrode to thesemi-transmissive and semi-reflective electrode is λ_(G). The light withthe wavelength λ_(B) is emitted from the second light-emitting element.In the second light-emitting element, the optical path length from thesecond reflective electrode to the second light-emitting layer is3λ_(B)/4 and the optical path length from the second reflectiveelectrode to the semi-transmissive and semi-reflective electrode isλ_(B). Light with the wavelength λ_(R) is emitted from the thirdlight-emitting element. In the third light-emitting element, the opticalpath length from the third reflective electrode to the firstlight-emitting layer is λ_(R)/4 and the optical path length from thethird reflective electrode to the semi-transmissive and semi-reflectiveelectrode is λ_(R)/2.

In each of the above structures, the EL layer includes one or more of ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer.

In each of the above structures, the first transparent conductive layeris thicker than the second transparent conductive layer.

In each of the above structures, light emitted from the firstlight-emitting element, light emitted from the second light-emittingelement, and light emitted from the third light-emitting element havewavelengths different from each other.

One embodiment of the present invention is an electronic appliance or alighting device which includes the light-emitting device.

According to one embodiment of the present invention, a light-emittingdevice and a lighting device each of which includes a plurality oflight-emitting elements exhibiting light with different wavelengths andutilizes a microcavity system can be provided. The light-emitting deviceand the lighting device each have an element structure in which lightwith a desired wavelength is emitted from each of the light-emittingelements by setting the optical path length from a reflective electrodeto a light-emitting layer (a light-emitting region) and the optical pathlength from the reflective electrode to a semi-transmissive andsemi-reflective electrode to the predetermined values. Thus, thelight-emitting elements can have favorable color purity and highlight-extraction efficiency. Further, according to one embodiment of thepresent invention, a transparent conductive layer does not need to beformed in a light-emitting element from which light with the longestwavelength is extracted; accordingly, the number of steps and the costcan be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 illustrates a light-emitting device according to one embodimentof the present invention;

FIGS. 2A and 2B illustrate a light-emitting device according to oneembodiment of the present invention;

FIG. 3 illustrates a light-emitting device according to one embodimentof the present invention;

FIGS. 4A and 4B illustrate a light-emitting device according to oneembodiment of the present invention;

FIGS. 5A to 5D illustrate electronic appliances;

FIG. 6 illustrates lighting devices;

FIG. 7 illustrates a light-emitting device according to one embodimentof the present invention; and

FIGS. 8A and 8B show results of measurement of emission spectra.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments and an example of the present invention will bedescribed in detail with reference to the drawings. Note that thepresent invention is not limited to the description below, and modes anddetails thereof can be modified in various ways without departing fromthe spirit and scope of the present invention. Therefore, the presentinvention should not be construed as being limited to the description inthe following embodiments and example. In addition, components denotedby the same reference numerals throughout the drawings are considered asthe same components, and repeated description thereof is omitted.

(Embodiment 1)

In this embodiment, a light-emitting device according to one embodimentof the present invention will be described with reference to FIG. 1.Note that hereinafter, an optical path length represents the thicknessof a component.

As illustrated in FIG. 1, the light-emitting device according to oneembodiment of the present invention includes light-emitting elements (afirst light-emitting element (G) 110G, a second light-emitting element(B) 110B, and a third light-emitting element (R) 110R) having differentstructures.

The first light-emitting element (G) 110G has a structure in which afirst transparent conductive layer 103 a; an EL layer 105 including afirst light-emitting layer (R) 104R, a second light-emitting layer (G)104G, and a third light-emitting layer (B) 104B in part; and asemi-transmissive and semi-reflective electrode 106 are sequentiallystacked over a reflective electrode 102. The second light-emittingelement (B) 110B has a structure in which a second transparentconductive layer 103 b, the EL layer 105, and the semi-transmissive andsemi-reflective electrode 106 are sequentially stacked over thereflective electrode 102. The third light-emitting element (R) 110R hasa structure in which the EL layer 105 and the semi-transmissive andsemi-reflective electrode 106 are sequentially stacked over thereflective electrode 102.

Note that the reflective electrode 102, the EL layer 105, and thesemi-transmissive and semi-reflective electrode 106 are common to thelight-emitting elements (the first light-emitting element (G) 1106, thesecond light-emitting element (B) 110B, and the third light-emittingelement (R) 110R). The first light-emitting layer (R) 104R emits light(λ_(R)) having a peak in a wavelength range from 600 nm to 760 nm. Thesecond light-emitting layer (G) 104G emits light (λ_(G)) having a peakin a wavelength range from 500 nm to 550 nm. The third light-emittinglayer (B) 104B emits light (λ_(B)) having a peak in a wavelength rangefrom 420 nm to 480 nm. Thus, in each of the light-emitting elements (thefirst light-emitting element (G) 110G, the second light-emitting element(B) 110B, and the third light-emitting element (R) 110R), light emittedfrom the first light-emitting layer (R) 104R, light emitted from thesecond light-emitting layer (G) 104G, and light emitted from the thirdlight-emitting layer (B) 104B overlap with each other; accordingly,light having a broad emission spectrum that covers a visible light rangecan be emitted. Note that the above wavelengths satisfy the relation ofλ_(B)<λ_(G)<λ_(R).

Each of the light-emitting elements described in this embodiment has astructure in which the EL layer 105 is interposed between the reflectiveelectrode 102 and the semi-transmissive and semi-reflective electrode106. Light emitted in all directions from the light-emitting layersincluded in the EL layer 105 is resonated by the reflective electrode102 and the semi-transmissive and semi-reflective electrode 106 whichfunction as a micro optical resonator (a microcavity). Note that thereflective electrode 102 is formed using a conductive material havingreflectivity, and a film whose visible light reflectivity is 40% to100%, preferably 70% to 100%, and whose resistivity is lower than orequal to 1×10⁻² Ωcm is used. In addition, the semi-transmissive andsemi-reflective electrode 106 is formed using a conductive materialhaving reflectivity and a conductive material having alight-transmitting property, and a film whose visible light reflectivityis 20% to 80%, preferably 40% to 70%, and whose resistivity is lowerthan or equal to 1×10⁻² Ωcm is used.

In this embodiment, the thicknesses of the transparent conductive layers(the first transparent conductive layer 103 a and the second transparentconductive layer 103 b) provided in the first light-emitting element (G)110G and the second light-emitting element (B) 110B, respectively, arevaried between the light-emitting elements, whereby the light-emittingelements differ in the optical path length from the reflective electrode102 to the semi-transmissive and semi-reflective electrode 106. In otherwords, in light having a broad emission spectrum, which is emitted fromthe light-emitting layers of each of the light-emitting elements, lightwith a wavelength that is resonated between the reflective electrode 102and the semi-transmissive and semi-reflective electrode 106 can beenhanced while light with a wavelength that is not resonatedtherebetween can be attenuated. Thus, when the elements differ in theoptical path length from the reflective electrode 102 to thesemi-transmissive and semi-reflective electrode 106, light withdifferent wavelengths can be extracted.

Note that the total thickness (optical path length) from the reflectiveelectrode 102 to the semi-transmissive and semi-reflective electrode 106is set to λ_(G) in the first light-emitting element (G) 110G; the totalthickness (optical path length) from the reflective electrode 102 to thesemi-transmissive and semi-reflective electrode 106 is set to in thesecond light-emitting element (B) 110B; and the total thickness (opticalpath length) from the reflective electrode 102 to the semi-transmissiveand semi-reflective electrode 106 is set to λ_(R)/2 in the thirdlight-emitting element (R) 110R.

In this manner, the light (λ_(G)) emitted from the second light-emittinglayer (G) 104G included in the EL layer 105 is mainly extracted from thefirst light-emitting element (G) 110G, the light (λ_(B)) emitted fromthe third light-emitting layer (B) 104B included in the EL layer 105 ismainly extracted from the second light-emitting element (B) 110B, andthe light (λ_(R)) emitted from the first light-emitting layer (R) 104Rincluded in the EL layer 105 is mainly extracted from the thirdlight-emitting element (R) 110R. Note that the light extracted from eachof the light-emitting elements is emitted through the semi-transmissiveand semi-reflective electrode 106 side.

In the above structure, the total thickness (optical path length) fromthe reflective electrode 102 to the semi-transmissive andsemi-reflective electrode 106 is set to λ_(R)/2 in the thirdlight-emitting element (R) 110R; if the total thickness (optical pathlength) from the reflective electrode 102 to the semi-transmissive andsemi-reflective electrode 106 is set to 4 in the third light-emittingelement (R) 110R, from which the light (λ_(R)) with the longestwavelength is extracted, the light (λ_(B)) is also resonated. Therefore,by setting the total thickness (optical path length) from the reflectiveelectrode 102 to the semi-transmissive and semi-reflective electrode 106to λ_(R)/2 in the third light-emitting element (R) 110R, only the light(λ_(R)) can be extracted. Note that even when the total thicknesses(optical path lengths) from the reflective electrode 102 to thesemi-transmissive and semi-reflective electrode 106 are set to λ_(G) andλ_(B) in the first light-emitting element (G) 110G and the secondlight-emitting element (B) 110B, respectively, from which light withwavelengths shorter than that of light from the third light-emittingelement (R) 110R is extracted, it is possible to extract only light withdesired wavelengths. Here, strictly speaking, the total thickness(optical path length) from the reflective electrode 102 to thesemi-transmissive and semi-reflective electrode 106 can be the totalthickness (optical path length) from a reflection region in thereflective electrode 102 to a reflection region in the semi-transmissiveand semi-reflective electrode 106. However, it is difficult to preciselydetermine the positions of the reflection regions in the reflectiveelectrode 102 and the semi-transmissive and semi-reflective electrode106; therefore, it is assumed that the above effect can be sufficientlyobtained wherever the reflection regions may be set in the reflectiveelectrode 102 and the semi-transmissive and semi-reflective electrode106. Note that the light extracted from each of the light-emittingelements does not necessarily have the same peak as the emitted light.For example, light having a peak at 460 nm may be emitted from thelight-emitting layer, and light having a peak at 450 nm may be extractedfrom the first light-emitting element (G) 110G.

Next, in the first light-emitting element (G) 110G, the optical pathlength from the reflective electrode 102 to the second light-emittinglayer (G) 104G is adjusted to a desired thickness (3λ_(G)/4); thus,light emitted from the second light-emitting layer (G) 104G can beamplified. Light (first reflected light) that is reflected by thereflective electrode 102 of the light emitted from the secondlight-emitting layer (G) 104G interferes with light (first incidentlight) that directly enters the semi-transmissive and semi-reflectiveelectrode 106 from the second light-emitting layer (G) 104G Therefore,by adjusting the optical path length from the reflective electrode 102to the second light-emitting layer (G) 104G to the desired value(3λ_(G)/4), the phases of the first reflected light and the firstincident light can be aligned with each other and the light emitted fromthe second light-emitting layer (G) 104G can be amplified.

Note that even when the optical path length from the reflectiveelectrode 102 to the second light-emitting layer (G) 104G is set toλ_(G)/4, the first incident light and the first reflected light areenhanced by interfering with each other; however, since the thickness ofthe first transparent conductive layer 103 a is larger than λ_(G)/4, theoptical path length is adjusted to the value 3λ_(G)/4 which is largerthan λ_(G)/4 and enables the first incident light and the firstreflected light to be enhanced by interfering with each other. Here,strictly speaking, the optical path length from the reflective electrode102 to the second light-emitting layer (G) 104G can be the optical pathlength from a reflection region in the reflective electrode 102 to alight-emitting region in the second light-emitting layer (G) 104EHowever, it is difficult to precisely determine the positions of thereflection region in the reflective electrode 102 and the light-emittingregion in the second light-emitting layer (G) 104G; therefore, it isassumed that the above effect can be sufficiently obtained wherever thereflection region and the light-emitting region may be set in thereflective electrode 102 and the second light-emitting layer (G) 1046,respectively.

Next, in the second light-emitting element (B) 110B, the optical pathlength from the reflective electrode 102 to the third light-emittinglayer (B) 104B is adjusted to a desired thickness (3λ_(R)/4); thus,light emitted from the third light-emitting layer (B) 104B can beamplified. Light (second reflected light) that is reflected by thereflective electrode 102 of the light emitted from the thirdlight-emitting layer (B) 104B interferes with light (second incidentlight) that directly enters the semi-transmissive and semi-reflectiveelectrode 106 from the third light-emitting layer (B) 104B. Therefore,by adjusting the optical path length from the reflective electrode 102to the third light-emitting layer (B) 104B to the desired value(3λ_(B)/4), the phases of the second reflected light and the secondincident light can be aligned with each other and the light emitted fromthe third light-emitting layer (B) 104B can be amplified.

Note that even when the optical path length from the reflectiveelectrode 102 to the third light-emitting layer (B) 104B is set toλ_(B)/4, the second incident light and the second reflected light areenhanced by interfering with each other; however, since the thickness ofthe second transparent conductive layer 103 b is larger than λ_(B)/4,the optical path length is adjusted to the value 3λ_(B)/4 which islarger than λ_(B)/4 and enables the second incident light and the secondreflected light to be enhanced by interfering with each other. Here,strictly speaking, the optical path length from the reflective electrode102 to the third light-emitting layer (B) 104B can be the optical pathlength from a reflection region in the reflective electrode 102 to alight-emitting region in the third light-emitting layer (B) 104B.However, it is difficult to precisely determine the positions of thereflection region in the reflective electrode 102 and the light-emittingregion in the third light-emitting layer (B) 104B; therefore, it isassumed that the above effect can be sufficiently obtained wherever thereflection region and the light-emitting region may be set in thereflective electrode 102 and the third light-emitting layer (B) 104B,respectively.

Next, in the third light-emitting element (R) 110R, the optical pathlength from the reflective electrode 102 to the first light-emittinglayer (R) 104R is adjusted to a desired thickness (λ_(R)/4); thus, lightemitted from the first light-emitting layer (R) 104R can be amplified.Light (third reflected light) that is reflected by the reflectiveelectrode 102 of the light emitted from the first light-emitting layer(R) 104R interferes with light (third incident light) that directlyenters the semi-transmissive and semi-reflective electrode 106 from thefirst light-emitting layer (R) 104R. Therefore, by adjusting the opticalpath length from the reflective electrode 102 to the firstlight-emitting layer (R) 104R to the desired value (λ_(R)/4), the phasesof the third reflected light and the third incident light can be alignedwith each other and the light emitted from the first light-emittinglayer (R) 104R can be amplified.

Note that, strictly speaking, the optical path length from thereflective electrode 102 to the first light-emitting layer (R) 104R inthe third light-emitting element can be the optical path length from areflection region in the reflective electrode 102 to a light-emittingregion in the first light-emitting layer (R) 104R. However, it isdifficult to precisely determine the positions of the reflection regionin the reflective electrode 102 and the light-emitting region in thefirst light-emitting layer (R) 104R; therefore, it is assumed that theabove effect can be sufficiently obtained wherever the reflection regionand the light-emitting region may be set in the reflective electrode 102and the first light-emitting layer (R) 104R, respectively.

With the above structure, light with wavelengths which differ among thelight-emitting elements including the same EL layer can be efficientlyextracted. Accordingly, a light-emitting device having favorable colorpurity and high light-extraction efficiency can be provided. Further,with the structure described in this embodiment, a transparentconductive layer does not need to be formed in the light-emittingelement from which light with the longest wavelength is extracted;accordingly, the number of steps and the cost can be reduced.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 2)

In this embodiment, a specific structure of the light-emitting deviceaccording to one embodiment of the present invention, which is describedin Embodiment 1, will be described with reference to FIGS. 2A and 2B.

A light-emitting device described in this embodiment includes a firstlight-emitting element (G) 210G in which a reflective electrode 202, afirst transparent conductive layer 203 a, an EL layer 205 including alight-emitting layer 204, and a semi-transmissive and semi-reflectiveelectrode 206 are sequentially stacked over a substrate 201; a secondlight-emitting element (B) 210B in which the reflective electrode 202, asecond transparent conductive layer 203 b, the EL layer 205 includingthe light-emitting layer 204, and the semi-transmissive andsemi-reflective electrode 206 are sequentially stacked over thesubstrate 201; and a third light-emitting element (R) 210R in which thereflective electrode 202, the EL layer 205 including the light-emittinglayer 204, and the semi-transmissive and semi-reflective electrode 206are sequentially stacked over the substrate 201.

Plastic (an organic resin), glass, quartz, or the like can be used forthe substrate 201. As an example of plastic, a member made ofpolycarbonate, polyarylate, polyethersulfone, or the like can be given.Plastic is preferably used for the substrate 201, in which case areduction in the weight of the light-emitting device can be achieved.Alternatively, a sheet with a high barrier property against water vaporand a high heat radiation property (e.g., a sheet containing diamondlike carbon (DLC)) can be used as the substrate 201.

Although not illustrated, an inorganic insulator may be provided overthe substrate 201. The inorganic insulator functions as a protectivelayer or a sealing film which blocks an external contaminant such aswater. By providing the inorganic insulator, deterioration of thelight-emitting element can be suppressed; thus, the durability andlifetime of the light-emitting device can be improved.

A single layer or a stack of a nitride film and a nitride oxide film canbe used as the inorganic insulator. Specifically, the inorganicinsulator can be formed using silicon oxide, silicon nitride, siliconoxynitride, aluminum oxide, aluminum nitride, aluminum oxynitride, orthe like by a CVD method, a sputtering method, or the like depending onthe material. It is preferable that the inorganic insulator be formedusing silicon nitride by a CVD method. The thickness of the inorganicinsulator may be approximately greater than or equal to 100 nm and lessthan or equal to 1 μm. Alternatively, an aluminum oxide film, a DLCfilm, a carbon film containing nitrogen, or a film containing zincsulfide and silicon oxide (a ZnS.SiO₂ film) may be used as the inorganicinsulator.

The reflective electrode 202 is formed using a conductive materialhaving reflectivity. Note that a film formed using the conductivematerial having reflectivity has a visible light reflectivity of 40% to100%, preferably 70% to 100%, and a resistivity lower than or equal to1×10⁻² Ωcm. As the material having reflectivity, a metal material suchas aluminum, gold, platinum, silver, nickel, tungsten, chromium,molybdenum, iron, cobalt, copper, or palladium can be used. In addition,any of the following can be used: alloys containing aluminum (aluminumalloys) such as an alloy of aluminum and titanium, an alloy of aluminumand nickel, and an alloy of aluminum and neodymium; and an alloycontaining silver such as an alloy of silver and copper. An alloy ofsilver and copper is preferable because of its high heat resistance.Further, a metal film or a metal oxide film is stacked on an aluminumalloy film, whereby oxidation of the aluminum alloy film can besuppressed. As examples of a material for the metal film or the metaloxide film, titanium and titanium oxide are given.

The first transparent conductive layer 203 a and the second transparentconductive layer 203 b are each formed to have a single-layer structureor a layered structure using a conductive material having alight-transmitting property. A film formed using the conductive materialhaving a light-transmitting property has a visible light transmittancehigher than or equal to 40% and a resistivity lower than or equal to1×10⁻² Ωcm. As the conductive material having a light-transmittingproperty, indium oxide (In₂O₃), tin oxide (SnO₂), zinc oxide (ZnO),indium oxide-tin oxide (In₂O₃—SnO₂, abbreviated as ITO), indiumoxide-zinc oxide (In₂O₃—ZnO, abbreviated as IZO), zinc oxide to whichgallium is added, any of these metal oxide materials containing siliconoxide, graphene, or the like can be used.

The first transparent conductive layer 203 a and the second transparentconductive layer 203 b can be formed using a conductive compositioncontaining a conductive macromolecule (also referred to as conductivepolymer). As the conductive macromolecule, a so-called π-electronconjugated conductive polymer can be used. For example, polyaniline or aderivative thereof, polypyrrole or a derivative thereof, polythiopheneor a derivative thereof, and a copolymer of two or more of aniline,pyrrole, and thiophene or a derivative thereof can be given.

Note that the thickness of each of the first transparent conductivelayer 203 a and the second transparent conductive layer 203 b needs tobe adjusted as appropriate in accordance with the wavelength of light tobe emitted from the light-emitting element. Therefore, the firsttransparent conductive layer 203 a in the first light-emitting element(G) 210G is formed to have a thickness which enables only light from asecond light-emitting layer (G) 204G to be emitted through thesemi-transmissive and semi-reflective electrode 206 side. The secondtransparent conductive layer 203 b in the second light-emitting element(B) 210B is formed to have a thickness which enables only light from athird light-emitting layer (B) 204B to be emitted through thesemi-transmissive and semi-reflective electrode 206 side.

Note that the reflective electrode 202, the first transparent conductivelayer 203 a, and the second transparent conductive layer 203 b can eachbe processed into a desired shape in a photolithography step and anetching step.

An insulating layer 207 formed using an insulating material is providedbetween the light-emitting elements so as to cover end portions of thereflective electrode 202, the first transparent conductive layer 203 a,and the second transparent conductive layer 203 b. The insulating layer207 can be formed to have a single-layer structure or a layeredstructure using an organic insulating material (a material containingpolyimide, polyamide, polyimideamide, benzocyclobutene, or siloxanepolymer as a main component), an inorganic insulating material (amaterial containing silicon oxide, silicon nitride, silicon oxynitride,or the like as a main component), or the like.

Further, the insulating layer 207 may be formed using a light-blockingmaterial that reflects or absorbs light. For example, a black organicresin can be used, which can be formed by mixing a black resin of apigment material, carbon black, titanium black, or the like into a resinmaterial such as photosensitive or non-photosensitive polyimide.Alternatively, a light-blocking metal film can be used, which may beformed using chromium, molybdenum, nickel, titanium, cobalt, copper,tungsten, or aluminum, for example. The insulating layer 207 having alight-blocking property can prevent light leakage to an adjacentlight-emitting element, which leads to high-contrast and high-definitiondisplay.

Note that there is no particular limitation on the method of forming theinsulating layer 207, and a dry method such as an evaporation method, asputtering method, or a CVD method or a wet method such as spin coating,dip coating, spray coating, a droplet discharging method (such as aninkjet method), screen printing, or offset printing may be useddepending on the material. As needed, an etching method (dry etching orwet etching) may be employed to form a desired pattern.

The EL layer 205 includes at least the light-emitting layer 204. Notethat the EL layer may include another functional layer in addition tothe light-emitting layer 204. Specifically, the EL layer 205 can have alayered structure including a hole-injection layer, a hole-transportlayer, an electron-transport layer, an electron-injection layer, acharge generation layer, and/or the like.

The hole-injection layer is a layer containing a substance having a highhole-injection property. As the substance having a high hole-injectionproperty, for example, a metal oxide such as molybdenum oxide, titaniumoxide, vanadium oxide, rhenium oxide, ruthenium oxide, chromium oxide,zirconium oxide, hafnium oxide, tantalum oxide, silver oxide, tungstenoxide, or manganese oxide can be used. Alternatively, aphthalocyanine-based compound such as phthalocyanine (abbreviation:H₂Pc) or copper(II) phthalocyanine (abbreviation: CuPc) can be used.

Further alternatively, any of the following aromatic amine compoundswhich are low molecular organic compounds can be used:4,4′,4″-tris(N,N-diphenylamino)triphenylamine (abbreviation: TDATA),4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: MTDATA),4,4′-bis[N-(4-diphenylaminophenyl)-N-phenylamino]biphenyl (abbreviation:DPAB),4,4′-bis(N-{4-[N′-(3-methylphenyl)-N′-phenylamino]phenyl}-N-phenylamino)biphenyl(abbreviation: DNTPD),1,3,5-tris[N-(4-diphenylaminophenyl)-N-phenylamino]benzene(abbreviation: DPA3B),3-[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA1),3,6-bis[N-(9-phenylcarbazol-3-yl)-N-phenylamino]-9-phenylcarbazole(abbreviation: PCzPCA2),3-[N-(1-naphthyl)-N-(9-phenylcarbazol-3-yl)amino]-9-phenylcarbazole(abbreviation: PCzPCN1), and the like.

Still further alternatively, a high molecular compound (such as anoligomer, a dendrimer, or a polymer) can be used. For example, thefollowing high molecular compounds can be given: poly(N-vinylcarbazole)(abbreviation: PVK), poly(4-vinyltriphenylamine) (abbreviation: PVTPA),poly[N-(4-{N-[4-(4-diphenylamino)phenyl]phenyl-N-phenylamino}phenyl)methacrylamide](abbreviation: PIPDMA), andpoly[N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine] (abbreviation:Poly-TPD). A high molecular compound to which acid is added, such aspoly(3,4-ethylenedioxythiophene)/poly(styrenesulfonic acid) (PEDOT/PSS)or polyaniline/poly(styrenesulfonic acid) (PAni/PSS), may be used.

In particular, it is preferable to use a composite material in which anacceptor substance is mixed with an organic compound having a highhole-transport property for the hole-injection layer. With the use ofthe composite material in which an acceptor substance is mixed with asubstance having a high hole-transport property, excellent holeinjection from an anode can be obtained, which results in a reduction inthe driving voltage of the light-emitting element. Such a compositematerial can be formed by co-evaporation of a substance having a highhole-transport property and an acceptor substance. When thehole-injection layer is formed using the composite material, holes areeasily injected into the EL layer 205 from the anode.

As the organic compound for the composite material, any of a variety ofcompounds such as aromatic amine compounds, carbazole derivatives,aromatic hydrocarbon, and high molecular compounds (such as oligomers,dendrimers, and polymers) can be used. The organic compound for thecomposite material is preferably an organic compound having a highhole-transport property. Specifically, a substance having a holemobility higher than or equal to 10⁻⁶ cm²/Vs is preferably used. Notethat other than the above substances, any substance that has a propertyof transporting more holes than electrons may be used. Organic compoundsthat can be used for the composite material will be specifically givenbelow.

Examples of the organic compound that can be used for the compositematerial include aromatic amine compounds such as TDATA, MTDATA, DPAB,DNTPD, DPA3B, PCzPCA1, PCzPCA2, PCzPCN1,4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB orα-NPD),N,N′-bis(3-methylphenyl)-N,N′-diphenyl-[1,1′-biphenyl]-4,4′-diamine(abbreviation: TPD), and4-phenyl-4′-(9-phenylfluoren-9-yl)triphenylamine (abbreviation: BPAFLP);and carbazole derivatives such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP), 1,3,5-tris[4-(N-carbazolyl)phenyl]benzene(abbreviation: TCPB), 9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: CzPA),9-phenyl-3-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation:PCzPA), and 1,4-bis[4-(N-carbazolyl)phenyl]-2,3,5,6-tetraphenylbenzene.

In addition, it is possible to use any of the following aromatichydrocarbon compounds: 2-tert-butyl-9,10-di(2-naphthyl)anthracene(abbreviation: t-BuDNA), 2-tert-butyl-9,10-di(1-naphthyl)anthracene,9,10-bis(3,5-diphenylphenyl)anthracene (abbreviation: DPPA),2-tert-butyl-9,10-bis(4-phenylphenyl)anthracene (abbreviation: t-BuDBA),9,10-di(2-naphthyl)anthracene (abbreviation: DNA),9,10-diphenylanthracene (abbreviation: DPAnth), 2-tert-butylanthracene(abbreviation: t-BuAnth), 9,10-bis(4-methyl-1-naphthyl)anthracene(abbreviation: DMNA),9,10-bis[2-(1-naphthyl)phenyl)-2-tert-butylanthracene,9,10-bis[2-(1-naphthyl)phenyl]anthracene, and2,3,6,7-tetramethyl-9,10-di(1-naphthyl)anthracene.

Further alternatively, an aromatic hydrocarbon compound such as2,3,6,7-tetramethyl-9,10-di(2-naphthyl)anthracene, 9,9′-bianthryl,10,10′-diphenyl-9,9′-bianthryl,10,10′-bis(2-phenylphenyl)-9,9′-bianthryl,10,10′-bis[(2,3,4,5,6-pentaphenyl)phenyl]-9,9′-bianthryl, anthracene,tetracene, rubrene, perylene, 2,5,8,11-tetra(tert-butyl)perylene,pentacene, coronene, 4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation:DPVBi), or 9,10-bis[4-(2,2-diphenylvinyl)phenyl]anthracene(abbreviation: DPVPA) can be used.

Examples of an electron acceptor include organic compounds such as7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane (abbreviation:F₄-TCNQ) and chloranil; and transition metal oxides. In addition, oxidesof metals belonging to Groups 4 to 8 in the periodic table can be given.Specifically, vanadium oxide, niobium oxide, tantalum oxide, chromiumoxide, molybdenum oxide, tungsten oxide, manganese oxide, and rheniumoxide are preferable because of their high electron-accepting property.Among these, molybdenum oxide is especially preferable because it isstable in the air, has a low hygroscopic property, and is easilyhandled.

Note that the hole-injection layer may be formed using a compositematerial of the high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD, and the electron acceptor.

The hole-transport layer is a layer containing a substance having a highhole-transport property. As the substance having a high hole-transportproperty, any of the following aromatic amine compounds can be used, forexample: NPB, TPD, BPAFLP,4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), and4,4′-bis[N-(spiro-9,9′-bifluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: BSPB). The substances mentioned here are mainly ones thathave a hole mobility higher than or equal to 10⁻⁶ cm²/Vs. Note thatother than the above substances, any substance that has a property oftransporting more holes than electrons may be used. The layer containinga substance having a high hole-transport property is not limited to asingle layer, and two or more layers containing any of the abovesubstances may be stacked.

A carbazole derivative such as CBP, CzPA, or PCzPA or an anthracenederivative such as t-BuDNA, DNA, or DPAnth may be used for thehole-transport layer.

Alternatively, a high molecular compound such as PVK, PVTPA, PTPDMA, orPoly-TPD can be used for the hole-transport layer.

The light-emitting layer 204 is a layer containing a light-emittingorganic compound. As the light-emitting organic compound, for example, afluorescent compound which exhibits fluorescence or a phosphorescentcompound which exhibits phosphorescence can be used. FIG. 2B illustratesthe details of the light-emitting layer 204 in FIG. 2A. As illustratedin the drawing, the light-emitting layer 204 has a structure in which afirst light-emitting layer (R) 204R, the second light-emitting layer (G)204G, and the third light-emitting layer (B) 204B are sequentiallystacked.

Note that examples of the fluorescent compound that can be used for thefirst light-emitting layer (R) 204R include materials for red lightemission, such asN,N,N′,N-′tetrakis(4-methylphenyl)tetracene-5,11-diamine (abbreviation:p-mPhTD), and7,14-diphenyl-N,N,N′,N′-tetrakis(4-methylphenyl)acenaphtho[1,2-a]fluoranthene-3,10-diamine(abbreviation: p-mPhAFD). Examples of the phosphorescent compoundinclude organometallic complexes such asbis[2-(2′-benzo[4,5-═]thienyl)pyridinato-N,C^(3′))iridium(III)acetylacetonate (abbreviation: Ir(btp)₂(acac)),bis(1-phenylisoquinolinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(piq)₂(acac),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)quinoxalinato]iridium(III)(abbreviation: Ir(Fdpq)₂(acac)),(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)),(dipivaloylmethanato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(dpm)), and2,3,7,8,12,13,17,18-octaethyl-21H,23H-porphyrinplatinum(II)(abbreviation: PtOEP).

Examples of the fluorescent compound that can be used for the secondlight-emitting layer (G) 204G include materials for green lightemission, such asN-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCABPhA),N-(9,10-diphenyl-2-anthryl)-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPAPA),N-[9,10-bis(1,1′-biphenyl-2-yl)-2-anthryl]-N,N′,N′-triphenyl-1,4-phenylenediamine(abbreviation: 2DPABPhA),N-[9,10-bis(1,1′-biphenyl-2-yl)]-N-[4-(9H-carbazol-9-yl)phenyl]-N-phenylanthracen-2-amine(abbreviation: 2YGABPhA), and N,N,9-triphenylanthracen-9-amine(abbreviation: DPhAPhA). Examples of the phosphorescent compound includetris(2-phenylpyridinato-N,C^(2′))iridium(III) (abbreviation: Ir(ppy)₃),bis(2-phenylpyridinato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(ppy)₂(acac)),bis(1,2-diphenyl-1H-benzimidazolato)iridium(III) acetylacetonate(abbreviation: Ir(pbi)₂(acac)), bis(benzo[h] quinolinato)iridium(III)acetylacetonate (abbreviation: Ir(bzq)₂(acac)), and tris(benzo[h]quinolinato)iridium(III) (abbreviation: Ir(bzq)₃).

Examples of the fluorescent compound that can be used for the thirdlight-emitting layer (B) 204B include materials for blue light emission,such asN,N′-bis[4-(9H-carbazol-9-yl)phenyl]-N,N′-diphenylstilbene-4,4′-diamine(abbreviation: YGA2S),4-(9H-carbazol-9-yl)-4′-(10-phenyl-9-anthryl)triphenylamine(abbreviation: YGAPA), and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA). Examples of the phosphorescent compound includebis[2-(4′,6′-difluorophenyppyridinato-N,C^(2′)]iridium(III)tetrakis(1-pyrazolyl)borate (abbreviation: FIr6),bis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III) picolinate(abbreviation: FIrpic),bis{2-[3′,5′-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate (abbreviation: Ir(CF₃ppy)₂(pic)), andbis[2-(4′,6′-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate (abbreviation: FIr(acac)).

In the case where a phosphorescent compound is used for each of thelayers in the light-emitting layer 204, the phosphorescent compound ispreferably dispersed in another substance serving as a host material. Asthe host material, various kinds of materials can be used, and it ispreferable to use a substance which has a lowest unoccupied molecularorbital level (LUMO level) higher than that of a light-emittingsubstance and has a highest occupied molecular orbital level (HOMOlevel) lower than that of the light-emitting substance.

Specific examples of the host material are as follows: a metal complexsuch as tris(8-quinolinolato)aluminum(III) (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum(III) (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium(II) (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum(III)(abbreviation: BAlq), bis(8-quinolinolato)zinc(II) (abbreviation: Znq),bis[2-(2-benzoxazolyl)phenolato]zinc(II) (abbreviation: ZnPBO), orbis[2-(2-benzothiazolyl)phenolato]zinc(II) (abbreviation: ZnBTZ); aheterocyclic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ),2,2′,2″-(1,3,5-benzenetriyfltris(1-phenyl-1H-benzimidazole)(abbreviation: TPBI), bathophenanthroline (abbreviation: BPhen), orbathocuproine (BCP); a condensed aromatic compound such as9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole (abbreviation: CzPA),3,6-diphenyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazole(abbreviation: DPCzPA), 9,10-bis(3,5-diphenylphenyflanthracene(abbreviation: DPPA), 9,10-di(2-naphthyl)anthracene (abbreviation: DNA),2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA),9,9′-bianthryl (abbreviation: BANT),9,9′-(stilbene-3,3′-diypdiphenanthrene (abbreviation: DPNS),9,9′-(stilbene-4,4′-diyl)diphenanthrene (abbreviation: DPNS2),3,3′,3″-(benzene-1,3,5-triyl)tripyrene (abbreviation: TPB3),9,10-diphenylanthracene (abbreviation: DPAnth), or6,12-dimethoxy-5,11-diphenylchrysene; and an aromatic amine compoundsuch asN,N-dipheyl-9-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: CzA1PA), 4-(10-phenyl-9-anthryl)triphenylamine(abbreviation: DPhPA),N,9-diphenyl-N-[4-(10-phenyl-9-anthryl)phenyl]-9H-carbazol-3-amine(abbreviation: PCAPA),N,9-diphenyl-N-{4-[4-(10-phenyl-9-anthryl)phenyl]phenyl}-9H-carbazol-3-amine(abbreviation: PCAPBA),N-(9,10-diphenyl-2-anthryl)-N,9-diphenyl-9H-carbazol-3-amine(abbreviation: 2PCAPA), NPB (or α-NPD), TPD, DFLDPBi, or BSPB.

Plural kinds of materials can be used as the host material. For example,in order to suppress crystallization, a substance such as rubrene whichsuppresses crystallization may be further added. In addition, NPB, Alq,or the like may be further added in order to efficiently transfer energyto the phosphorescent compound serving as a guest material.

Note that when a structure in which a guest material is dispersed in ahost material is employed, crystallization of the layers in thelight-emitting layer 204 can be suppressed. Further, concentrationquenching due to high concentration of the guest material can besuppressed.

The electron-transport layer is a layer containing a substance having ahigh electron-transport property. As the substance having a highelectron-transport property, the following metal complexes having aquinoline skeleton or a benzoquinoline skeleton can be given, forexample: tris(8-quinolinolato)aluminum (abbreviation: Alq),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂), andbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq). Alternatively, a metal complex or the like including anoxazole-based or thiazole-based ligand, such asbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(BOX)₂) orbis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂) canbe used. Besides the metal complexes,2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-biphenylyl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole(abbreviation: TAZ), bathophenanthroline (abbreviation: BPhen),bathocuproine (abbreviation: BCP), or the like can also be used. Thesubstances mentioned here are mainly ones that have an electron mobilityhigher than or equal to 10⁻⁶ cm²/Vs. Further, the electron-transportlayer is not limited to a single layer, and two or more layerscontaining any of the above substances may be stacked.

The electron-injection layer is a layer containing a substance having ahigh electron-injection property. For the electron-injection layer, analkali metal, an alkaline earth metal, or a compound thereof, such aslithium, cesium, calcium, lithium fluoride, cesium fluoride, calciumfluoride, or lithium oxide, can be used. A rare earth metal compoundsuch as erbium fluoride can also be used. Further, any of the abovesubstances for forming the electron-transport layer can be used.

Charges are generated in the charge generation layer by applying voltageto the light-emitting element. The charge generation layer has functionsof injecting holes into the EL layer from the cathode side and injectingelectrons into the EL layer from the anode side.

Note that the charge generation layer can be formed using the abovecomposite material in which an acceptor substance is mixed with anorganic compound having a high hole-transport property. Further, thecharge generation layer may have a layered structure including a layercontaining the composite material and a layer containing anothermaterial.

In addition, the EL layer 205 can be formed by any of a variety ofmethods such as an evaporation method using an evaporation mask, adroplet discharging method like an inkjet method, a printing method, anda spin coating method.

The semi-transmissive and semi-reflective electrode 206 is formed usinga combination (e.g., a layered film) of a thin film (preferably having athickness less than or equal to 20 nm, further preferably having athickness less than or equal to 10 nm) of a conductive material havingreflectivity and a film of a conductive material having alight-transmitting property. Note that the film included in thesemi-transmissive and semi-reflective electrode 206 has a visible lightreflectivity of 20% to 80%, preferably 40% to 70%, and a resistivitylower than or equal to 1×10⁻² Ωcm.

As the conductive material having reflectivity and the conductivematerial having a light-transmitting property used for thesemi-transmissive and semi-reflective electrode 206, any of the abovematerials can be used.

In this embodiment, the reflective electrode 202 and the firsttransparent conductive layer 203 a function as an anode and thesemi-transmissive and semi-reflective electrode 206 functions as acathode in the first light-emitting element (G) 210G. The reflectiveelectrode 202 and the second transparent conductive layer 203 b functionas an anode and the semi-transmissive and semi-reflective electrode 206functions as a cathode in the second light-emitting element (B) 210B.The reflective electrode 202 functions as an anode and thesemi-transmissive and semi-reflective electrode 206 functions as acathode in the third light-emitting element (R) 210R.

As described above, the optical path lengths differ among the firstlight-emitting element (G) 210G, the second light-emitting element (B)210B, and the third light-emitting element (R) 210R in thelight-emitting device described in this embodiment, so that only lightwith a desired spectrum can be extracted from each of the light-emittingelement by utilizing a microcavity and light with a desired wavelengthcan be amplified. Accordingly, a light-emitting device having favorablecolor purity and high light-extraction efficiency can be provided.Further, with the structure described in this embodiment, a transparentconductive layer does not need to be formed in the light-emittingelement from which light with the longest wavelength is extracted;accordingly, the number of steps and the cost can be reduced.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 3)

In this embodiment, a structure of a light-emitting element included ina light-emitting device according to one embodiment of the presentinvention will be described with reference to FIG. 3. Note thathereinafter, an optical path length represents the thickness of acomponent.

As illustrated in FIG. 3, the light-emitting device according to oneembodiment of the present invention includes light-emitting elements (afirst light-emitting element (G) 310G, a second light-emitting element(B) 310B, and a third light-emitting element (R) 310R) having differentstructures.

The first light-emitting element (G) 310G has a structure in which afirst transparent conductive layer 303 a; an EL layer 305 including afirst light-emitting layer (Y) 304Y and a second light-emitting layer(B) 304B in part; and a semi-transmissive and semi-reflective electrode306 are sequentially stacked over a reflective electrode 302. The secondlight-emitting element (B) 310B has a structure in which a secondtransparent conductive layer 303 b, the EL layer 305, and thesemi-transmissive and semi-reflective electrode 306 are sequentiallystacked over the reflective electrode 302. The third light-emittingelement (R) 310R has a structure in which the EL layer 305 and thesemi-transmissive and semi-reflective electrode 306 are sequentiallystacked over the reflective electrode 302.

Note that the reflective electrode 302, the EL layer 305, and thesemi-transmissive and semi-reflective electrode 306 are common to thelight-emitting elements (the first light-emitting element (G) 310G, thesecond light-emitting element (B) 310B, and the third light-emittingelement (R) 310R). The first light-emitting layer (Y) 304Y emits light(λ_(Y)) having a peak in a wavelength range from 550 nm to 570 nm. Thesecond light-emitting layer (B) 304B emits light (λ_(B)) having a peakin a wavelength range from 420 nm to 480 nm. Thus, in each of thelight-emitting elements (the first light-emitting element (G) 310G, thesecond light-emitting element (B) 310B, and the third light-emittingelement (R) 310R), light emitted from the first light-emitting layer (Y)304Y and light emitted from the second light-emitting layer (B) 304Boverlap with each other; accordingly, light having a broad emissionspectrum that covers a visible light range can be emitted. Note that theabove wavelengths satisfy the relation of λ_(B)<_(Y).

Each of the light-emitting elements described in this embodiment has astructure in which the EL layer 305 is interposed between the reflectiveelectrode 302 and the semi-transmissive and semi-reflective electrode306. Light emitted in all directions from the light-emitting layersincluded in the EL layer 305 is resonated by the reflective electrode302 and the semi-transmissive and semi-reflective electrode 306 whichfunction as a micro optical resonator (a microcavity). Note that thereflective electrode 302 is formed using a conductive material havingreflectivity, and a film whose visible light reflectivity is 40% to100%, preferably 70% to 100%, and whose resistivity is lower than orequal to 1×10⁻² Ωcm is used. In addition, the semi-transmissive andsemi-reflective electrode 306 is formed using a conductive materialhaving reflectivity and a conductive material having alight-transmitting property, and a film whose visible light reflectivityis 20% to 80%, preferably 40% to 70%, and whose resistivity is lowerthan or equal to 1×10⁻² Ωcm is used.

In this embodiment, the thicknesses of the transparent conductive layers(the first transparent conductive layer 303 a and the second transparentconductive layer 303 b) provided in the first light-emitting element (G)310G and the second light-emitting element (B) 310B, respectively, arevaried between the light-emitting elements, whereby the light-emittingelements differ in the optical path length from the reflective electrode302 to the semi-transmissive and semi-reflective electrode 306. In otherwords, in light having a broad emission spectrum, which is emitted fromthe light-emitting layers of each of the light-emitting elements, lightwith a wavelength that is resonated between the reflective electrode 302and the semi-transmissive and semi-reflective electrode 306 can beenhanced while light with a wavelength that is not resonatedtherebetween can be attenuated. Thus, when the elements differ in theoptical path length from the reflective electrode 302 to thesemi-transmissive and semi-reflective electrode 306, light withdifferent wavelengths can be extracted.

Note that the total thickness (optical path length) from the reflectiveelectrode 302 to the semi-transmissive and semi-reflective electrode 306is set to λ_(G) in the first light-emitting element (G) 310G; the totalthickness (optical path length) from the reflective electrode 302 to thesemi-transmissive and semi-reflective electrode 306 is set to λ_(B) inthe second light-emitting element (B) 310B; and the total thickness(optical path length) from the reflective electrode 302 to thesemi-transmissive and semi-reflective electrode 306 is set to λ_(R)/2 inthe third light-emitting element (R) 310R.

In this manner, light (λ_(G)) emitted from the first light-emittinglayer (Y) 304Y included in the EL layer 305 is mainly extracted from thefirst light-emitting element (G) 310G, the light (λ_(B)) emitted fromthe second light-emitting layer (B) 304B included in the EL layer 305 ismainly extracted from the second light-emitting element (B) 310B, andlight (λ_(R)) emitted from the first light-emitting layer (Y) 304Yincluded in the EL layer 305 is mainly extracted from the thirdlight-emitting element (R) 310R. Note that the light (λ_(G)) has a peakin a wavelength range from 500 nm to 550 nm, the light (λ_(B)) has apeak in a wavelength range from 420 nm to 480 nm, and the light (λ_(R))has a peak in a wavelength range from 600 nm to 760 nm. In addition, thelight extracted from each of the light-emitting elements is emittedthrough the semi-transmissive and semi-reflective electrode 306 side.

In the above structure, the total thickness (optical path length) fromthe reflective electrode 302 to the semi-transmissive andsemi-reflective electrode 306 is set to λ_(R)/2 in the thirdlight-emitting element (R) 310R; if the total thickness (optical pathlength) from the reflective electrode 302 to the semi-transmissive andsemi-reflective electrode 306 is set to λ_(R) in the thirdlight-emitting element (R) 310R, from which the light (λ_(R)) with thelongest wavelength is extracted, the light (λ_(B)) is also resonated.Therefore, by setting the total thickness (optical path length) from thereflective electrode 302 to the semi-transmissive and semi-reflectiveelectrode 306 to λ_(R)/2 in the third light-emitting element (R) 310R,only the light (λ_(R)) can be extracted. Note that even when the totalthicknesses (optical path lengths) from the reflective electrode 302 tothe semi-transmissive and semi-reflective electrode 306 are set to λ_(G)and λ_(B) in the first light-emitting element (G) 310G and the secondlight-emitting element (B) 310B, respectively, from which light withwavelengths shorter than that of light from the third light-emittingelement (R) 310R is extracted, it is possible to extract only lighthaving peaks at desired wavelengths. Here, strictly speaking, the totalthickness (optical path length) from the reflective electrode 302 to thesemi-transmissive and semi-reflective electrode 306 can be the totalthickness (optical path length) from a reflection region in thereflective electrode 302 to a reflection region in the semi-transmissiveand semi-reflective electrode 306. However, it is difficult to preciselydetermine the positions of the reflection region in the reflectiveelectrode 302 and the reflection region in the semi-transmissive andsemi-reflective electrode 306; therefore, it is assumed that the aboveeffect can be sufficiently obtained wherever the reflection regions maybe set in the reflective electrode 302 and the semi-transmissive andsemi-reflective electrode 306.

Next, in the first light-emitting element (G) 310G, the optical pathlength from the reflective electrode 302 to the first light-emittinglayer (Y) 304Y is adjusted to a desired thickness (3λ_(G)/4); thus,light with λ_(G) of light emitted from the first light-emitting layer(Y) 304Y can be amplified. Light (first reflected light) that isreflected by the reflective electrode 302 of the light emitted from thefirst light-emitting layer (Y) 304Y interferes with light (firstincident light) that directly enters the semi-transmissive andsemi-reflective electrode 306 from the first light-emitting layer (Y)304Y. Therefore, by adjusting the optical path length from thereflective electrode 302 to the first light-emitting layer (Y) 304Y tothe desired value (3λ_(G)/4), the phases of the first reflected lightand the first incident light can be aligned with each other and thelight with λ_(G) of the light emitted from the first light-emittinglayer (Y) 304Y can be amplified.

Note that even when the optical path length from the reflectiveelectrode 302 to the first light-emitting layer (Y) 304Y is set toλ_(G)/4, the first incident light and the first reflected light areenhanced by interfering with each other; however, since the thickness ofthe first transparent conductive layer 303 a is larger than λ_(G)/4, theoptical path length is adjusted to the value 3λ_(G)/4 which is largerthan λ_(G)/4 and enables the first incident light and the firstreflected light to be enhanced by interfering with each other. Here,strictly speaking, the optical path length from the reflective electrode302 to the first light-emitting layer (Y) 304Y can be the optical pathlength from a reflection region in the reflective electrode 302 to alight-emitting region in the first light-emitting layer (Y) 304Y.However, it is difficult to precisely determine the positions of thereflection region in the reflective electrode 302 and the light-emittingregion in the first light-emitting layer (Y) 304Y; therefore, it isassumed that the above effect can be sufficiently obtained wherever thereflection region and the light-emitting region may be set in thereflective electrode 302 and the first light-emitting layer (Y) 304Y,respectively.

Next, in the second light-emitting element (B) 310B, the optical pathlength from the reflective electrode 302 to the second light-emittinglayer (B) 304B is adjusted to a desired thickness (3λ_(R)/4); thus,light emitted from the second light-emitting layer (B) 304B can beamplified. Light (second reflected light) that is reflected by thereflective electrode 302 of the light emitted from the secondlight-emitting layer (B) 304B interferes with light (second incidentlight) that directly enters the semi-transmissive and semi-reflectiveelectrode 306 from the second light-emitting layer (B) 304B. Therefore,by adjusting the optical path length from the reflective electrode 302to the second light-emitting layer (B) 304B to the desired value(3λ_(R)/4), the phases of the second reflected light and the secondincident light can be aligned with each other and the light emitted fromthe second light-emitting layer (B) 304B can be amplified.

Note that even when the optical path length from the reflectiveelectrode 302 to the second light-emitting layer (B) 304B is set toλ_(B)/4, the second incident light and the second reflected light areenhanced by interfering with each other; however, since the thickness ofthe second transparent conductive layer 303 b is larger than λ_(B)/4,the optical path length is adjusted to the value 3λ_(B)/4 which islarger than λ_(B)/4 and enables the second incident light and the secondreflected light to be enhanced by interfering with each other. Here,strictly speaking, the optical path length from the reflective electrode302 to the second light-emitting layer (B) 304B can be the optical pathlength from a reflection region in the reflective electrode 302 to alight-emitting region in the second light-emitting layer (B) 304B.However, it is difficult to precisely determine the positions of thereflection region in the reflective electrode 302 and the light-emittingregion in the second light-emitting layer (B) 304B; therefore, it isassumed that the above effect can be sufficiently obtained wherever thereflection region and the light-emitting region may be set in thereflective electrode 302 and the second light-emitting layer (B) 304B,respectively.

Next, in the third light-emitting element (R) 310R, the optical pathlength from the reflective electrode 302 to the first light-emittinglayer (Y) 304Y is adjusted to a desired thickness (λ_(R)/4); thus, lightwith λ_(R) of light emitted from the first light-emitting layer (Y) 304Ycan be amplified. Light (third reflected light) that is reflected by thereflective electrode 302 of the light emitted from the firstlight-emitting layer (Y) 304Y interferes with light (third incidentlight) that directly enters the semi-transmissive and semi-reflectiveelectrode 306 from the first light-emitting layer (Y) 304Y. Therefore,by adjusting the optical path length from the reflective electrode 302to the first light-emitting layer (Y) 304Y to the desired value(λ_(R)/4), the phases of the third reflected light and the thirdincident light can be aligned with each other and the light with λ_(R)of the light emitted from the first light-emitting layer (Y) 304Y can beamplified.

Note that, strictly speaking, the optical path length from thereflective electrode 302 to the first light-emitting layer (Y) 304Y inthe third light-emitting element can be the optical path length from areflection region in the reflective electrode 302 to a light-emittingregion in the first light-emitting layer (Y) 304Y. However, it isdifficult to precisely determine the positions of the reflection regionin the reflective electrode 302 and the light-emitting region in thefirst light-emitting layer (Y) 304Y; therefore, it is assumed that theabove effect can be sufficiently obtained wherever the reflection regionand the light-emitting region may be set in the reflective electrode 302and the first light-emitting layer (Y) 304Y, respectively.

This embodiment is different from Embodiments 1 and 2 only in that thefirst light-emitting layer (Y) 304Y and the second light-emitting layer(B) 304B are formed in the EL layer 305. Thus, the description inEmbodiments 1 and 2 can be referred to for the same portions.

As for the first light-emitting layer (Y) 304Y, examples of afluorescent compound that can be used for the first light-emitting layer(Y) 304Y include rubrene, and5,12-bis(1,1′-biphenyl-4-yl)-6,11-diphenyltetracene (abbreviation: BPT).Examples of a phosphorescent compound includebis(2,4-diphenyl-1,3-oxazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(dpo)₂(acac)),bis[2-(4′-(perfluorophenylphenyl)pyridinato]iridium(III) acetylacetonate(abbreviation: Ir(p-PF-ph)₂(acac)),bis(2-phenylbenzothiazolato-N,C^(2′))iridium(III) acetylacetonate(abbreviation: Ir(bt)₂(acac)),(acetylacetonato)bis[2,3-bis(4-fluorophenyl)-5-methylpyrazinato]iridium(III)(abbreviation: Ir(Fdppr-Me)₂(acac)), and(acetylacetonato)bis{2-(4-methoxyphenyl)-3,5-dimethylpyrazinato}iridium(III)(abbreviation: Ir(dmmoppr)₂(acac)).

In addition, the second light-emitting layer (B) 304B can be formedusing any of the substances given as examples of a substance that can beused for the third light-emitting layer (B) 204B in Embodiment 2.

With the above structure, light with wavelengths which differ among thelight-emitting elements including the same EL layer can be efficientlyextracted. Accordingly, a light-emitting device having favorable colorpurity and high light-extraction efficiency can be provided. Further,with the structure described in this embodiment, a transparentconductive layer does not need to be formed in the light-emittingelement from which light with the longest wavelength is extracted;accordingly, the number of steps and the cost can be reduced.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 4)

In this embodiment, a specific structure of a light-emitting deviceaccording to one embodiment of the present invention will be describedwith reference to FIGS. 4A and 4B. FIG. 4A is a top view illustrating alight-emitting device, and FIG. 4B is a cross-sectional view along lineA-A′ and line B-B′ in FIG. 4A.

In FIG. 4A, reference numeral 401 denotes a driver circuit portion (asource line driver circuit), reference numeral 402 denotes a pixelportion, and reference numeral 403 denotes a driver circuit portion (agate line driver circuit), which are shown by a dotted line. Referencenumeral 404 denotes a sealing substrate, reference numeral 405 denotes asealant, and a portion enclosed by the sealant 405 is a space 407.

Note that a lead wiring 408 is a wiring for transmitting signals thatare to be input to the source line driver circuit 401 and the gate linedriver circuit 403, and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from a flexible printed circuit(FPC) 409 which serves as an external input tettninal. Although only theFPC is illustrated here, a printed wiring board (PWB) may be attached tothe FPC. The light-emitting device in this specification includes notonly a light-emitting device itself but also a light-emitting device towhich an FPC or a PWB is attached.

Next, a cross-sectional structure will be described with reference toFIG. 4B. The driver circuit portions and the pixel portion are formedover an element substrate 410. Here, the source line driver circuit 401which is the driver circuit portion and three light-emitting elements(418G, 418B, and 418R) in the pixel portion 402 are illustrated. Notethat as the source line driver circuit 401, a CMOS circuit which isobtained by combining an n-channel TFT 423 and a p-channel TFT 424 isformed. The driver circuit may be formed using a variety of circuitssuch as a CMOS circuit, a PMOS circuit, and an NMOS circuit. Although adriver-integrated type in which a driver circuit is formed over asubstrate is described in this embodiment, one embodiment of the presentinvention is not limited to this type, and the driver circuit can beformed outside the substrate.

Further, the pixel portion 402 includes TFTs (411G, 411B, and 411R) andthe plurality of light-emitting elements (418G, 418B, and 418R) whichinclude a reflective electrode 412 (stacked with a transparentconductive layer 413, depending on the light-emitting element)electrically connected to drains of the TFTs, an EL layer 416, and asemi-transmissive and semi-reflective electrode 417. Note that aninsulating layer 414 is formed to cover end portions of the reflectiveelectrode 412 (and the transparent conductive layer 413 in the casewhere the transparent conductive layer is stacked thereover).

The insulating layer 414 is preferably formed so as to have a curvedsurface with curvature at an upper end portion or a lower end portionthereof in order to obtain favorable coverage. For example, whenpositive photosensitive acrylic is used as a material for the insulatinglayer 414, only an upper end portion of the insulating layer 414 canhave a curved surface with a radius of curvature (0.2 μm to 3 μm).Alternatively, the insulating layer 414 can be formed using either anegative type photosensitive material that becomes insoluble in anetchant by light irradiation or a positive type photosensitive materialthat becomes soluble in an etchant by light irradiation.

The transparent conductive layer 413, the EL layer 416, and thesemi-transmissive and semi-reflective electrode 417 are formed over thereflective electrode 412 in accordance with the structure of thelight-emitting element. Here, the materials given in Embodiment 2 can beused as materials for the reflective electrode 412, the transparentconductive layer 413, the EL layer 416, and the semi-transmissive andsemi-reflective electrode 417.

In addition, the EL layer 416 is formed by any of a variety of methodssuch as an evaporation method using an evaporation mask, a dropletdischarging method like an inkjet method, a printing method, and a spincoating method.

The sealing substrate 404 is attached to the element substrate 410 withthe sealant 405; thus, the light-emitting elements 418G, 418B, and 418Rare provided in the space 407 enclosed by the element substrate 410, thesealing substrate 404, and the sealant 405. Note that the space 407 isfilled with a filler, and may be filled with an inert gas (such asnitrogen or argon) or the sealant 405.

Note that as the sealant 405, an epoxy-based resin is preferably used.It is preferable that such a material do not transmit moisture or oxygenas much as possible. The sealing substrate 404 can be formed using aglass substrate; a quartz substrate; or a plastic substrate made offiberglass-reinforced plastics (FRP), polyvinyl fluoride (PVF),polyester, acrylic, or the like.

In the above manner, the active matrix light-emitting device accordingto one embodiment of the present invention can be obtained. Note thatthe light-emitting device according to one embodiment of the presentinvention can be a passive matrix light-emitting device as well as theabove active matrix light-emitting device.

Note that in the light-emitting device according to one embodiment ofthe present invention, light with wavelengths which differ among thelight-emitting elements including the same EL layer can be efficientlyextracted. Accordingly, a light-emitting device having favorable colorpurity and high light-extraction efficiency can be provided. Further,with the structure described in this embodiment, a transparentconductive layer does not need to be formed in a light-emitting elementfrom which light with the longest wavelength is extracted; accordingly,the number of steps and the cost can be reduced.

The structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 5)

In this embodiment, examples of a variety of electronic appliances thatare completed using a light-emitting device according to one embodimentof the present invention will be described with reference to FIGS. 5A to5D.

Examples of the electronic appliances to which the light-emitting deviceis applied are a television device (also referred to as television ortelevision receiver), a monitor of a computer or the like, a camerassuch as a digital camera or a digital video camera, a digital photoframe, a mobile phone (also referred to as cellular phone or cellularphone device), a portable game machine, a portable information terminal,an audio reproducing device, and a large-sized game machine such as apachinko machine. Specific examples of these electronic appliances areillustrated in FIGS. 5A to 5D.

FIG. 5A illustrates an example of a television set. In a television set7100, a display portion 7103 is incorporated in a housing 7101. Imagescan be displayed on the display portion 7103, and the light-emittingdevice can be used for the display portion 7103. In addition, here, thehousing 7101 is supported by a stand 7105.

The television set 7100 can be operated by an operation switch of thehousing 7101 or a separate remote controller 7110. With operation keys7109 of the remote controller 7110, channels and volume can becontrolled and images displayed on the display portion 7103 can becontrolled. Furthelluore, the remote controller 7110 may be providedwith a display portion 7107 for displaying data output from the remotecontroller 7110.

Note that the television set 7100 is provided with a receiver, a modem,and the like. With the receiver, a general television broadcast can bereceived. Furthermore, when the television set 7100 is connected to acommunication network by wired or wireless connection via the modem,one-way (from a transmitter to a receiver) or two-way (between atransmitter and a receiver, between receivers, or the like) datacommunication can be performed.

FIG. 5B illustrates a computer having a main body 7201, a housing 7202,a display portion 7203, a keyboard 7204, an external connection port7205, a pointing device 7206, and the like. Note that this computer ismanufactured using the light-emitting device for the display portion7203.

FIG. 5C illustrates a portable game machine having two housings, ahousing 7301 and a housing 7302, which are connected with a jointportion 7303 so that the portable game machine can be opened or folded.A display portion 7304 is incorporated in the housing 7301, and adisplay portion 7305 is incorporated in the housing 7302. In addition,the portable game machine illustrated in FIG. 5C includes a speakerportion 7306, a recording medium insertion portion 7307, an LED lamp7308, input means (an operation key 7309, a connection terminal 7310, asensor 7311 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), and a microphone 7312), and thelike. Needless to say, the structure of the portable game machine is notlimited to the above as long as the light-emitting device is used for atleast one of the display portion 7304 and the display portion 7305, andmay include other accessories as appropriate. The portable game machineillustrated in FIG. 5C has a function of reading out a program or datastored in a storage medium to display it on the display portion, and afunction of sharing information with another portable game machine bywireless communication. The portable game machine illustrated in FIG. 5Ccan have a variety of functions without limitation to the above.

FIG. 5D illustrates an example of a mobile phone. A mobile phone 7400 isprovided with a display portion 7402 incorporated in a housing 7401,operation buttons 7403, an external connection port 7404, a speaker7405, a microphone 7406, and the like. Note that the mobile phone 7400is manufactured using the light-emitting device for the display portion7402.

When the display portion 7402 of the mobile phone 7400 illustrated inFIG. 5D is touched with a finger or the like, data can be input to themobile phone 7400. Further, operations such as making a call andcomposing an e-mail can be performed by touching the display portion7402 with a finger or the like.

There are mainly three screen modes of the display portion 7402. Thefirst mode is a display mode mainly for displaying images. The secondmode is an input mode mainly for inputting data such as text. The thirdmode is a display-and-input mode in which two modes of the display modeand the input mode are combined.

For example, in the case of making a call or composing an e-mail, a textinput mode mainly for inputting text is selected for the display portion7402 so that text displayed on the screen can be input. In this case, itis preferable to display a keyboard or number buttons on almost theentire screen of the display portion 7402.

When a detection device including a sensor for detecting inclination,such as a gyroscope or an acceleration sensor, is provided inside themobile phone 7400, display on the screen of the display portion 7402 canbe automatically switched by determining the orientation of the mobilephone 7400 (whether the mobile phone is placed horizontally orvertically for a landscape mode or a portrait mode).

The screen modes are switched by touching the display portion 7402 oroperating the operation buttons 7403 of the housing 7401. The screenmodes can also be switched depending on the kind of image displayed onthe display portion 7402. For example, when a signal of an imagedisplayed on the display portion is a signal of moving image data, thescreen mode is switched to the display mode. When the signal is a signalof text data, the screen mode is switched to the input mode.

Moreover, in the input mode, when input by touching the display portion7402 is not performed for a certain period while a signal detected by anoptical sensor in the display portion 7402 is detected, the screen modemay be controlled so as to be switched from the input mode to thedisplay mode.

The display portion 7402 may function as an image sensor. For example,an image of a palm print, a fingerprint, or the like is taken when thedisplay portion 7402 is touched with the palm or the finger, wherebypersonal authentication can be performed. Further, by providing abacklight or a sensing light source which emits near-infrared light inthe display portion, an image of a finger vein, a palm vein, or the likecan be taken.

As described above, the electronic appliances can be obtained byapplication of the light-emitting device according to one embodiment ofthe present invention. The light-emitting device has a remarkably wideapplication range, and can be applied to electronic appliances in avariety of fields.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

(Embodiment 6)

In this embodiment, examples of a lighting device to which alight-emitting device according to one embodiment of the presentinvention is applied will be described with reference to FIG. 6.

FIG. 6 illustrates an example in which the light-emitting deviceaccording to one embodiment of the present invention is used as anindoor lighting device 8001. Since the light-emitting device can have alarger area, it can be used for a lighting device having a large area.In addition, a lighting device 8002 in which a light-emitting region hasa curved surface can also be obtained with the use of a housing with acurved surface. A light-emitting element included in the light-emittingdevice described in this embodiment is in a thin film form, which allowsthe housing to be designed more freely. Therefore, the lighting devicecan be elaborately designed in a variety of ways. Further, a wall of theroom may be provided with a large-sized lighting device 8003.

Moreover, the light-emitting device according to one embodiment of thepresent invention can be used for a table by being used as a surface ofa table 8004. By being used as part of other furniture, thelight-emitting device can be used as the furniture.

As described above, the light-emitting device according to oneembodiment of the present invention can be used for variousapplications. Note that in the light-emitting device according to oneembodiment of the present invention, light with wavelengths which differamong light-emitting elements including the same EL layer can beefficiently extracted. Accordingly, a light-emitting device havingfavorable color purity and high light-extraction efficiency can beprovided. Further, a transparent conductive layer does not need to beformed in a light-emitting element from which light with the longestwavelength is extracted; accordingly, the number of steps and the costcan be reduced.

Note that the structure described in this embodiment can be combined asappropriate with any of the structures described in the otherembodiments.

[Example]

In this example, a light-emitting device (1) was fabricated such thatthe total thickness (optical path length) from a reflective electrode702 to a semi-transmissive and semi-reflective electrode 706 was λ_(R)in a light-emitting element from which light (λ_(R)) having a peak in awavelength range from 600 nm to 760 nm was emitted. Further, alight-emitting device (2) was fabricated such that the total thickness(optical path length) from the reflective electrode 302 to thesemi-transmissive and semi-reflective electrode 306 was λ_(R)/2 in alight-emitting element from which the light (λ_(R)) was emitted as inthe above embodiment. Results of measurement of emission spectra in thelight-emitting devices will be shown.

The light-emitting device (1) in this example has a structureillustrated in FIG. 7, and includes different light-emitting elements (afirst′ light-emitting element (R) 710R, a second′ light-emitting element(G) 710G, and a third′ light-emitting element (B) 710B).

The first′ light-emitting element (R) 710R has a structure in which afirst transparent conductive layer 703 a; an EL layer 705 including afirst light-emitting layer (Y) 704Y and a second light-emitting layer(B) 704B in part; and the semi-transmissive and semi-reflectiveelectrode 706 are sequentially stacked over the reflective electrode702. The second′ light-emitting element (G) 710G has a structure inwhich a second transparent conductive layer 703 b, the EL layer 705, andthe semi-transmissive and semi-reflective electrode 706 are sequentiallystacked over the reflective electrode 702. The third′ light-emittingelement (B) 710B has a structure in which the EL layer 705 and thesemi-transmissive and semi-reflective electrode 706 are sequentiallystacked over the reflective electrode 702.

The reflective electrode 702, the EL layer 705, and thesemi-transmissive and semi-reflective electrode 706 are common to thelight-emitting elements (the first′ light-emitting element (R) 710R, thesecond′ light-emitting element (G) 710G, and the third′ light-emittingelement (B) 710B). The first light-emitting layer (Y) 704Y emits light(λ_(Y)) having a peak in a wavelength range from 550 nm to 570 nm. Thesecond light-emitting layer (B) 704B emits light (λ_(B)) having a peakin a wavelength range from 420 nm to 480 nm Thus, in each of thelight-emitting elements (the first′ light-emitting element (R) 710R, thesecond′ light-emitting element (G) 710G, and the third′ light-emittingelement (B) 710B), light emitted from the first light-emitting layer (Y)704Y and light emitted from the second light-emitting layer (B) 704Boverlap with each other; accordingly, light having a broad emissionspectrum that covers a visible light range can be emitted. Note that theabove wavelengths satisfy the relation of λ_(B)<λ_(Y).

In the light-emitting device (1), the total thickness (optical pathlength) from the reflective electrode 702 to the semi-transmissive andsemi-reflective electrode 706 is set to λ_(R) in the first′light-emitting element (R) 710R; the total thickness (optical pathlength) from the reflective electrode 702 to the semi-transmissive andsemi-reflective electrode 706 is set to λ_(G) in the second′light-emitting element (G) 710G; and the total thickness (optical pathlength) from the reflective electrode 702 to the semi-transmissive andsemi-reflective electrode 706 is set to λ_(B) in the third′light-emitting element (B) 710B. Note that the first′ light-emittingelement (R) 710R is a light-emitting element from which light with λ_(R)is mainly emitted; the second′ light-emitting element (G) 710G is alight-emitting element from which light with λ_(G) is mainly emitted;and the third′ light-emitting element (B) 710B is a light-emittingelement from which light with λ_(B) is mainly emitted.

In addition, in the light-emitting device (1), the total thickness(optical path length) from the reflective electrode 702 to the firstlight-emitting layer (Y) 704Y is set to 3λ_(R)/4 in the first′light-emitting element (R) 710R; the total thickness (optical pathlength) from the reflective electrode 702 to the first light-emittinglayer (Y) 704Y is set to 3λ_(G)/4 in the second′ light-emitting element(G) 710G; and the total thickness (optical path length) from thereflective electrode 702 to the second light-emitting layer (B) 704B isset to λ_(R)/4 in the third′ light-emitting element (B) 710B.

The light-emitting device (2) in this example has the structureillustrated in FIG. 3 in Embodiment 3, and includes differentlight-emitting elements (the first light-emitting element (G) 310G, thesecond light-emitting element (B) 310B, and the third light-emittingelement (R) 310R).

In the light-emitting device (2), the first light-emitting element (G)310G has a structure in which the first transparent conductive layer 303a; the EL layer 305 including the first light-emitting layer (Y) 304Yand the second light-emitting layer (B) 304B in part; and thesemi-transmissive and semi-reflective electrode 306 are sequentiallystacked over the reflective electrode 302. The second light-emittingelement (B) 310B has a structure in which the second transparentconductive layer 303 b, the EL layer 305, and the semi-transmissive andsemi-reflective electrode 306 are sequentially stacked over thereflective electrode 302. The third light-emitting element (R) 310R hasa structure in which the EL layer 305 and the semi-transmissive andsemi-reflective electrode 306 are sequentially stacked over thereflective electrode 302.

The reflective electrode 302, the EL layer 305, and thesemi-transmissive and semi-reflective electrode 306 are common to thelight-emitting elements (the first light-emitting element (G) 310G, thesecond light-emitting element (B) 310B, and the third light-emittingelement (R) 310R). The first light-emitting layer (Y) 304Y emits light(λ_(Y)) having a peak in a wavelength range from 550 nm to 570 nm. Thesecond light-emitting layer (B) 304B emits light (λ_(B)) having a peakin a wavelength range from 420 nm to 480 nm.

In the light-emitting device (2), the total thickness (optical pathlength) from the reflective electrode 302 to the semi-transmissive andsemi-reflective electrode 306 is set to λ_(G) in the firstlight-emitting element (G) 310G; the total thickness (optical pathlength) from the reflective electrode 302 to the semi-transmissive andsemi-reflective electrode 306 is set to λ_(B) in the secondlight-emitting element (B) 310B; and the total thickness (optical pathlength) from the reflective electrode 302 to the semi-transmissive andsemi-reflective electrode 306 is set to λ_(R)/2 in the thirdlight-emitting element (R) 310R. Note that the first light-emittingelement (G) 310G is a light-emitting element from which light with λ_(G)is mainly emitted; the second light-emitting element (B) 310B is alight-emitting element from which light with λ_(B) is mainly emitted;and the third light-emitting element (R) 310R is a light-emittingelement from which light with λ_(R) is mainly emitted.

In addition, in the light-emitting device (2), the total thickness(optical path length) from the reflective electrode 302 to the firstlight-emitting layer (Y) 304Y is set to 3λ_(G)/4 in the firstlight-emitting element (G) 310G; the total thickness (optical pathlength) from the reflective electrode 302 to the second light-emittinglayer (B) 304B is set to 3λ_(R)/4 in the second light-emitting element(B) 310B; and the total thickness (optical path length) from thereflective electrode 302 to the first light-emitting layer (Y) 304Y isset to λ_(R)/4 in the third light-emitting element (R) 310R.

Specific methods of manufacturing the light-emitting device (1) and thelight-emitting device (2) will be described below. Note that thefollowing description is common to the light-emitting device (1) and thelight-emitting device (2) unless otherwise stated, and differentportions will be pointed out as appropriate.

First, a layered film including a titanium-aluminum (Ti—Al) alloy filmand a titanium oxide (TiO₂) film was formed over a glass substrate by asputtering method, so that the reflective electrode 702 (302) wasformed. Note that the thickness of the reflective electrode 702 (302)was 110 nm. In this example, the reflective electrode 702 (302) wasformed as an anode.

Next, a transparent conductive layer was formed. In each of thelight-emitting device (1) and the light-emitting device (2), the firsttransparent conductive layer (703 a or 303 a) and the second transparentconductive layer (703 b or 303 b) were formed using indium tin oxidecontaining silicon oxide (ITSO) by a sputtering method. The thicknessesof the layers are shown below.

In the light-emitting device (1), the first transparent conductive layer703 a of the first′ light-emitting element (R) 710R was formed to athickness of 90 nm, and the second transparent conductive layer 703 b ofthe second′ light-emitting element (G) 710G was formed to a thickness of45 nm. A transparent conductive layer was not formed in the third′light-emitting element (B) 710B. In the light-emitting device (2), thefirst transparent conductive layer 303 a of the first light-emittingelement (G) 310G was formed to a thickness of 90 nm, and the secondtransparent conductive layer 303 b of the second light-emitting element(B) 310B was formed to a thickness of 45 nm. A transparent conductivelayer was not formed in the third light-emitting element (R) 310R. Inthe light-emitting device (1), the first′ light-emitting element (R)710R exhibits red light, the second′ light-emitting element (G) 710Gexhibits green light, and the third′ light-emitting element (B) 710Bexhibits blue light. In the light-emitting device (2), the firstlight-emitting element (G) 310G exhibits green light, the secondlight-emitting element (B) 310B exhibits blue light, and the thirdlight-emitting element (R) 310R exhibits red light.

Next, the EL layer 705 (305) including a stack of a plurality of layerswas formed over the reflective electrode 702 (302). In this example, theEL layer 705 (305) has a structure in which a hole-injection layer, ahole-transport layer, the first light-emitting layer (Y) 704Y (304Y)serving as a light-emitting layer, the second light-emitting layer (B)704B (304B) serving as a light-emitting layer, an electron-transportlayer, and an electron-injection layer are sequentially stacked.

The substrate provided with the reflective electrode 702 (302) was fixedto a substrate holder which was provided in a vacuum evaporationapparatus so that a surface provided with the reflective electrode 702(302) faced downward. The pressure in the vacuum evaporation apparatuswas reduced to approximately 10⁻⁴ Pa. Then, on the reflective electrode702 (302), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation:NPB or α-NPD) and molybdenum(VI) oxide were co-evaporated to form ahole-injection layer. The thicknesses of the hole-injection layers were120 nm and 50 nm in the light-emitting device (1) and the light-emittingdevice (2), respectively. The evaporation rate was adjusted such thatthe weight ratio of NPB to molybdenum oxide was 2:0.222 (=NPB:molybdenumoxide). Note that a co-evaporation method refers to an evaporationmethod in which evaporation is carried out from a plurality ofevaporation sources at the same time in one treatment chamber.

Next, a hole-transport material was deposited on the hole-injectionlayer to a thickness of 10 nm by an evaporation method using resistanceheating to form a hole-transport layer. Note that NPB (abbreviation) wasused for the hole-transport layer.

Next, the first light-emitting layer (Y) 704Y (304Y) serving as alight-emitting layer was formed over the hole-transport layer by anevaporation method using resistance heating. In the formation of thefirst light-emitting layer (Y) 704Y (304Y), a film was formed to athickness of 20 nm by co-evaporation using9-phenyl-9′-[4-10-phenyl-9-anthryl)phenyl]-3,3′-bi(9H-carbazole)(abbreviation: PCCPA) as a host material and rubrene as a guestmaterial. Note that the evaporation rate was adjusted such that theweight ratio of PCCPA (abbreviation) to rubrene was 1:0.01 (=PCCPA(abbreviation):rubrene).

Further, the second light-emitting layer (B) 704B (304B) was formed overthe first light-emitting layer (Y) 704Y (304Y). In the formation of thesecond light-emitting layer (B) 704B (304B), a film was formed to athickness of 30 nm by co-evaporation using9-[4-(N-carbazolyl)]phenyl-10-phenylanthracene (abbreviation: CzPA) as ahost material and4-(10-phenyl-9-anthryl)-4′-(9-phenyl-9H-carbazol-3-yl)triphenylamine(abbreviation: PCBAPA) as a guest material. Note that the evaporationrate was adjusted such that the weight ratio of CzPA (abbreviation) toPCBAPA (abbreviation) was 1:0.1 (=CzPA (abbreviation):PCBAPA(abbreviation)).

Furthermore, over the second light-emitting layer (B) 704B (304B), a10-nm-thick film of tris(8-quinolinolato)aluminum(III) (abbreviation:Alq) and, thereover, a 20-nm-thick film of bathophenanthroline(abbreviation: BPhen) in a case of the light-emitting device (1) and a10-nm-thick film of bathophenanthroline (abbreviation: BPhen) in a caseof the light-emitting device (2) were formed by an evaporation methodusing resistance heating to form an electron-transport layer.

Then, a lithium fluoride (LiF) film was formed to a thickness of 1 nmover the electron-transport layer to form an electron-injection layer.

Finally, a magnesium-silver alloy (Mg—Ag alloy, Mg:Ag=0.05:0.5) film wasformed by an evaporation method using resistance heating. Thethicknesses of the magnesium-silver alloy films were 10 nm and 15 nm inthe light-emitting device (1) and the light-emitting device (2),respectively. Further, a film of indium tin oxide containing siliconoxide (ITSO) was formed. The thicknesses of the films of indium tinoxide containing silicon oxide were 50 nm and 90 nm in thelight-emitting device (1) and the light-emitting device (2),respectively. As the semi-transmissive and semi-reflective electrode 706(306), the layered film including the magnesium-silver alloy film andthe film of indium tin oxide containing silicon oxide was used. In thismanner, the light-emitting device (1) and the light-emitting device (2)were fabricated.

Table 1 shows the element structures of the light-emitting device (1)and the light-emitting device (2) obtained in the above manner.

TABLE 1 semi- Trans- EL layer transmissive Light- parent Hole- Hole-First light- Second light- Electron- Electron- and semi- emittingReflective conductive injection transport emitting emitting layertransport injection reflective element electrode layer layer layer layer(Y) (B) layer layer electrode Light 1′ Ti Al TD₂ ITSO NPB MoOx NPB PCCPACzPA Alq BPhen LF Mg:Ag ITSO emitting 50 200 3 90 nm (1′) (20.222) 10 nmRubrene PCBAPA 10 20 nm 1 nm (0.05:0.5) 50 nm device (1)* 2′ nm nm nmITSO 120 nm (10.01) (10.1) nm 10 nm 45 nm (2′) 20 nm 30 nm 3′ —Reference — 702 703a (1′) 705 706 numeral 703b (2′) — — 704Y 704B — —Light 1  Ti Al TD₂ ITSO NPB MoOx NPB PCCPA CzPA Alq BPhen LF emitting 50200 3 90 nm (1′) (20.222) 10 nm Rubrene PCBAPA 10 10 nm 1 nm device(2)** 2  nm nm nm ITSO  50 nm (10.01) (10.1) nm Mg:Ag ITSO 45 nm (2′) 20nm 30 nm (0.05:0.5) 90 nm 3  — 15 nm Reference — 302 303a (1′) 305 306numeral 303b (2′) — — 304Y 304B — — *The case where the optical pathlengths from the reflective electrode to the semi-transmissive andsemi-reflective electrode are λ_(R) and λ_(B) in the light-emittingelement (R) exhibiting light with λ_(R) and the light-emitting element(B) exhibiting light with λ_(B), respectively. **The case where theoptical path lengths from the reflective electrode to thesemi-transmissive and semi-reflective electrode are λ_(R)/2 and λ_(B) inthe light-emitting element (R) exhibiting light with λ_(R) and thelight-emitting element (B) exhibiting light with λ_(B), respectively.Note that in this table, the first to third light-emitting elements aredenoted by light-emitting elements 1 to 3, respectively; the first′ tothird′ light-emitting elements are denoted by light-emitting elements 1′to 3′, respectively.

FIGS. 8A and 8B show results of measurement of emission spectra in thelight-emitting device (1) and the light-emitting device (2),respectively, which were fabricated in this example.

As is obvious from the results of the spectrum measurement, in thelight-emitting device (1) including the first′ light-emitting element(R) 710R in which the total thickness (optical path length) from thereflective electrode 702 to the semi-transmissive and semi-reflectiveelectrode 706 was set to λ_(R), the emission spectrum of the first′light-emitting element (R) 710R has two kinds of peak in the vicinity of460 nm and the in the vicinity of 610 nm. In contrast, in thelight-emitting device (2) including the third light-emitting element (R)310R in which the total thickness (optical path length) from thereflective electrode 302 to the semi-transmissive and semi-reflectiveelectrode 306 was set to λ_(R)/2, the emission spectrum of the thirdlight-emitting element (R) 310R has only one kind of peak in thevicinity of 610 nm.

Thus, the results indicate that, by setting the total thickness (opticalpath length) from a reflective electrode to a semi-transmissive andsemi-reflective electrode to λ_(R)/2 in a light-emitting element fromwhich light with λ_(R) is mainly emitted, light with different emissionspectrum peaks can be prevented from being emitted from onelight-emitting element.

This application is based on Japanese Patent Application serial no.2011-085922 filed with the Japan Patent Office on Apr. 8, 2011, theentire contents of which are hereby incorporated by reference.

What is claimed is:
 1. A light-emitting device comprising: a firstlight-emitting element including a first reflective electrode, a firsttransparent conductive layer in contact with the first reflectiveelectrode, an EL layer in contact with the first transparent conductivelayer, and a semi-transmissive and semi-reflective electrode in contactwith the EL layer; a second light-emitting element including a secondreflective electrode, a second transparent conductive layer in contactwith the second reflective electrode, the EL layer in contact with thesecond transparent conductive layer, and the semi-transmissive andsemi-reflective electrode in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode in contact with the ELlayer, wherein the EL layer includes a light-emitting layer emittinglight with a wavelength λR, wherein the light with the wavelength λR isemitted from the third light-emitting element, and wherein, in the thirdlight-emitting element, an optical path length from the third reflectiveelectrode to the light-emitting layer is λR/4 and an optical path lengthfrom the third reflective electrode to the semi-transmissive andsemi-reflective electrode is λR/2.
 2. The light-emitting deviceaccording to claim 1, wherein the EL layer includes one or more of ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer.
 3. The light-emitting deviceaccording to claim 1, wherein the first transparent conductive layer isthicker than the second transparent conductive layer.
 4. Thelight-emitting device according to claim 1, wherein light emitted fromthe first light-emitting element, light emitted from the secondlight-emitting element, and light emitted from the third light-emittingelement have wavelengths different from each other.
 5. Thelight-emitting device according to claim 1, wherein the first, secondand third reflective electrodes are formed using a same material.
 6. Anelectronic appliance comprising the light-emitting device according toclaim
 1. 7. A lighting device comprising the light-emitting deviceaccording to claim
 1. 8. A light-emitting device comprising: a firstlight-emitting element including a first reflective electrode, a firsttransparent conductive layer in contact with the first reflectiveelectrode, an EL layer in contact with the first transparent conductivelayer, and a semi-transmissive and semi-reflective electrode in contactwith the EL layer; a second light-emitting element including a secondreflective electrode, a second transparent conductive layer in contactwith the second reflective electrode, the EL layer in contact with thesecond transparent conductive layer, and the semi-transmissive andsemi-reflective electrode in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode in contact with the ELlayer, wherein the EL layer includes a first light-emitting layeremitting light with a wavelength λR, a second light-emitting layeremitting light with a wavelength λG, and a third light-emitting layeremitting light with a wavelength λB, where a wavelength relation ofλR>λG>λB is satisfied, wherein the light with the wavelength λG isemitted from the first light-emitting element, wherein, in the firstlight-emitting element, an optical path length from the first reflectiveelectrode to the second light-emitting layer is 3λG/4 and an opticalpath length from the first reflective electrode to the semi-transmissiveand semi-reflective electrode is λG, wherein the light with thewavelength λB is emitted from the second light-emitting element,wherein, in the second light-emitting element, an optical path lengthfrom the second reflective electrode to the third light-emitting layeris 3λB/4 and an optical path length from the second reflective electrodeto the semi-transmissive and semi-reflective electrode is λB, whereinthe light with the wavelength λR is emitted from the thirdlight-emitting element, and wherein, in the third light-emittingelement, an optical path length from the third reflective electrode tothe first light-emitting layer is λR/4 and an optical path length fromthe third reflective electrode to the semi-transmissive andsemi-reflective electrode is λR/2.
 9. The light-emitting deviceaccording to claim 8, wherein the EL layer includes one or more of ahole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer.
 10. The light-emitting deviceaccording to claim 8, wherein the first transparent conductive layer isthicker than the second transparent conductive layer.
 11. Thelight-emitting device according to claim 8, wherein light emitted fromthe first light-emitting element, light emitted from the secondlight-emitting element, and light emitted from the third light-emittingelement have wavelengths different from each other.
 12. Thelight-emitting device according to claim 8, wherein the first, secondand third reflective electrodes are formed using a same material.
 13. Anelectronic appliance comprising the light-emitting device according toclaim
 8. 14. A lighting device comprising the light-emitting deviceaccording to claim
 8. 15. A light-emitting device comprising: a firstlight-emitting element including a first reflective electrode, a firsttransparent conductive layer in contact with the first reflectiveelectrode, an EL layer in contact with the first transparent conductivelayer, and a semi-transmissive and semi-reflective electrode in contactwith the EL layer; and a second light-emitting element including asecond reflective electrode, the EL layer in contact with the secondreflective electrode, and the semi-transmissive and semi-reflectiveelectrode in contact with the EL layer, wherein the EL layer includes alight-emitting layer emitting light with a wavelength λR, wherein thelight with the wavelength XR is emitted from the second light-emittingelement, and wherein, in the second light-emitting element, an opticalpath length from the second reflective electrode to the light-emittinglayer is λR/4 and an optical path length from the second reflectiveelectrode to the semi-transmissive and semi-reflective electrode isλR/2.
 16. The light-emitting device according to claim 15, wherein theEL layer includes one or more of a hole-injection layer, ahole-transport layer, an electron-transport layer, and anelectron-injection layer.
 17. The light-emitting device according toclaim 15, wherein light emitted from the first light-emitting elementand light emitted from the second light-emitting element havewavelengths different from each other.
 18. The light-emitting deviceaccording to claim 15, wherein the first and second reflectiveelectrodes are formed using a same material.
 19. An electronic appliancecomprising the light-emitting device according to claim
 15. 20. Alighting device comprising the light-emitting device according to claim15.
 21. A light-emitting device comprising: a first light-emittingelement including a first reflective electrode, a first transparentconductive layer in contact with the first reflective electrode, an ELlayer in contact with the first transparent conductive layer, and asemi-transmissive and semi-reflective electrode in contact with the ELlayer; a second light-emitting element including a second reflectiveelectrode, a second transparent conductive layer in contact with thesecond reflective electrode, the EL layer in contact with the secondtransparent conductive layer, and the semi-transmissive andsemi-reflective electrode in contact with the EL layer; and a thirdlight-emitting element including a third reflective electrode, the ELlayer in contact with the third reflective electrode, and thesemi-transmissive and semi-reflective electrode in contact with the ELlayer, wherein the light with the wavelength λ1 is emitted from thefirst light-emitting element wherein the light with the wavelength λ2 isemitted from the second light-emitting element wherein the light withthe wavelength λ3 is emitted from the third light-emitting element,wherein a wavelength relation of λ3>λ1>λ2 is satisfied, wherein anoptical path length from the first reflective electrode to thesemi-transmissive and semi-reflective electrode in the firstlight-emitting element is longer than an optical path length from thethird reflective electrode to the semi-transmissive and semi-reflectiveelectrode in the third light-emitting element, and wherein an opticalpath length from the second reflective electrode to thesemi-transmissive and semi-reflective electrode in the secondlight-emitting element is longer than the optical path length from thethird reflective electrode to the semi-transmissive and semi-reflectiveelectrode in the third light-emitting element.
 22. The light-emittingdevice according to claim 21, wherein the EL layer includes one or moreof a hole-injection layer, a hole-transport layer, an electron-transportlayer, and an electron-injection layer.
 23. The light-emitting deviceaccording to claim 21, wherein the first transparent conductive layer isthicker than the second transparent conductive layer.
 24. Thelight-emitting device according to claim 21, wherein the first, secondand third reflective electrodes are formed using a same material.
 25. Anelectronic appliance comprising the light-emitting device according toclaim
 21. 26. A lighting device comprising the light-emitting deviceaccording to claim 21.